The present invention relates to a communication system for a wireless bar code reader used for the point of sales (POS) system and the management of physical distribution or production.
The conventional communication system of the wireless bar code reader includes, as disclosed in JP-A 2-224194, a wireless bar code reader transmitter containing a bar code reader section therein and a receiver for receiving data from the transmitter and transmitting the data thus received to a host computer. Each of the transmitter and the receiver contains both a radio transmitting section and a radio receiving section. In such configuration, the communication is performed by using the answering method wherein the transmission of data is confirmed between the radio transmitting section and the radio receiving section of the transmitter and those of the receiver such that the receiver returns an acknowledge (ACK) signal when the data is received normally, but returns a non-acknowledge (NAK) signal when the data is received erroneously.
In particular, since the wireless system mostly employed in the wireless bar code reader uses weak radio wave which is small in the radio wave intensity, such a system has employed the answering method so as to improve the communication accuracy.
FIG. 5 is a diagram showing an arrangement of the conventional communication system for the wireless bar code reader. In FIG. 5, when an operator depresses a reading start switch 1, a power is supplied to a wireless bar code reader transmitter from a power source section 2. An image signal of a bar code is output from an optical section 3, and the image signal of the bar code is interpreted as data by an interpretation section 4. The data thus interpreted is sent to a radio-frequency transmitting section 5, which in turn modulates the data into a radio signal with a constant carrier frequency. The radio signal thus modulated is radiated to the air from a transmitter antenna 6. The radio signal radiated in the air is received by a receiver antenna 7 of a receiver and the radio signal thus received is demodulated and converted in reception data by a radio-frequency receiving section 8. The reception data thus received is subjected to the error detection and the error correction by a control section 9.
When the data is received normally, the control section 9 returns an ACK (acknowledge) signal to a radio-frequency transmitting section 10 and also transmits the reception data to a host computer. The ACK signal is modulated in a radio signal with a constant carrier frequency by the radio-frequency transmitting section 10, and the radio signal thus modulated is radiated in the air from the receiver antenna 7. The radio signal radiated in the air is received by the transmitter antenna 6 of the wireless bar code reader transmitter, then the received signal is demodulated by a radio-frequency receiving section 11 and sent to the interpretation section 4. The interpretation section 4 makes a transmission completion indication section 12 indicate the completion of the data transmission and then the power source section 2 cuts off the power.
When the data is not received normally, the control section 9 returns a NAK (non-acknowledge) signal to the radio-frequency transmitting section 10, which in turn modulates the NAK signal in a radio signal with a constant carrier frequency. The radio signal thus modulated is radiated in the air from the receiver antenna 7. The radio signal radiated in the air is received by the transmitter antenna 6 of the wireless bar code reader transmitter, then modulated by the radio-frequency receiving section 11 and sent to the interpretation section 4. Then, the interpretation section 4 resends the data.
However, since each of the transmitter and the receiver of the conventional communication system of the wireless bar code reader contains therein both the radio transmitting section and the radio receiving section, the consumption power of the system is large and further it is difficult to miniaturize the system. In particular, since the radio receiver is large in the size of a circuit arrangement, which obstructs the miniaturization of the system.
Further, when the communication system of the wireless bar code reader is arranged in a manner that the wireless bar code reader transmitter containing a bar code reader section is provided with only the radio transmission section and the receiver for transmitting data to the host computer is provided with only the radio receiving section, such a system can not employ the answering method for returning the ACK and NAK signals. As a consequence, such a system has the disadvantage that the communication accuracy is degraded and lack of data transmission as to data read by a bar code may occur.
Further, in such a system, since the radio communication takes time, it takes much time from the reading of a bar code to the completion of data transmission to the receiver. Accordingly, such a system requires much time for operation.